Anti-Spam SMTP Proxy Server implements multiple spam filters
Anti Spam SMTP Gateway
CIDRAM: Classless Inter-Domain Routing Access Manager.
Remote anti spam utility
Mod of the original Faucet-in-a-Box faucet PHP script
Open Source Anti-Spam and Anti-Virus Gateway
ASP or PHP Captcha, completly configurable, with prevalidation
Prevent anonymous users from posting URLs in public notes.
Report spam to SpamCop.